i) Field of the Invention
This invention relates to a formed thermoplastic resin article. More specifically, the present invention is concerned with a formed article of a resin combined with a specific elastic polymer and also to a composition useful for the formed article. This invention also pertains to a process for the production of such a formed article.
The term "formed article" as used herein should be interpreted in a broad sense so that it can embrace not only molded articles but also extruded or otherwise shaped articles.
The present invention has made it possible to provide formed resin articles of improved impact strength while retaining good surface appearance and other good physical properties.
ii) Description of the Related Art
Thermoplastic resins are used in a wide variety of fields, for example, as parts or components (hereinafter called collectively "component" or "components") for home electric and electronic appliances and automotive vehicles because of their good formability, i.e., moldability or the like and the good surface appearance of articles formed therefrom.
In these fields, each component is required to have a certain degree of strength, for example, to prevent its breakage even when dropped, to retain various functions during daily use and/or to ensure safety to the human body.
In particular, formed resin articles employed as exterior components are required to have both good surface appearance and high strength so that thermoplastic resins for such articles have been-improved in various ways with respect to their impact strength.
A variety of methods are practiced with a view to improving the impact strength of a thermoplastic resin, including blending a particular thermoplastic resin with another thermoplastic resin to provide a polymer alloy having improved impact strength (Japanese Patent Laid-Open Nos. 240158/1990 and 26740/1991), broadening the molecular weight distribution of a specific thermoplastic resin to improve its impact strength (Japanese Patent Publication Nos. 73583/1991 and 42379/1990), or adding a particular additive to a thermoplastic resin to improve its impact strength (Japanese Patent Laid-Open No. 65060/1985 and U.S. Pat. No. 4,532,306).
It is also commonly practiced to improve the impact strength of a thermoplastic resin by dispersing an elastic polymer in various forms in the thermoplastic resin.
In styrene resins, for example, there are known HIPS resins (high-impact polystyrene resins) obtained by blending an elastic polymer, such as styrene-graft-polymerized polybutadiene or block SBR, in GPPS resin (general-purpose polystyrene resin); and ABS resins obtained by blending an elastic polymer, such as acrylonitrile- or styrene-graft-polymerized polybutadiene or block SBR, in AS resin.
With respect to polyolefin resins, on the other hand, it is known to improve the impact strength of PP resin or PE resin by blending an elastic polymer such as EPM or EPDM in it.
To improve the impact strength of a thermoplastic resin by using such an elastic polymer, the elastic polymer is added by (1) either polymerizing or blending the elastic component during polymerization of the thermoplastic resin itself or (2) incorporating the elastic polymer upon processing the thermoplastic resin into a resin composition.
In connection with the method (1), varies improved methods have been proposed over many years. Examples of known methods include to disperse an elastic polymer in a greater amount in a thermoplastic resin or to control an elastic polymer to a specific particle size distribution prior to its dispersion (Japanese Patent Laid-Open No. 156709/1985, Japanese Patent Laid-Open No. 47051/1985, etc.) and to distribute an elastic polymer in which a thermoplastic resin has been polymerized at an increased graft ratio to improve the compatibility with the thermoplastic resin to be used (Japanese Patent Laid-Open No. 58453/1976).
On the other hand, known examples of the method (2) include to incorporate by a kneader, extruder or the like one of various elastic polymers, which are compatible with a thermoplastic resin, in an amount sufficient to impart desired physical properties (Japanese Patent Laid-Open No. 200151/1986; Japanese Patent Publication Nos. 25975/1992 and 6656/1989).
The approach which involves mixing and dispersion of an elastic polymer in a thermoplastic resin to improve the impact strength of the latter can generally improve the impact strength in proportion to an increase in the proportion of the elastic polymer but, on the other hand, is accompanied by the drawbacks that physical properties of an article, such as surface gloss, rigidity and heat resistance, are deteriorated or the flowability is substantially lowered upon forming. It has therefore remained as a difficult goal for many years to provide a formed thermoplastic resin article with improved impact strength while retaining good external appearance and various good physical properties.